I didn't use USAA but AAA and like FlyNavy, I didn't stick with the "selected" dealers. I thought the prices sounded too good to be true as well and was sure there was some hidden fee or that they'd try to really undervalue my trade. I went to one of those dealerships to get a written quote, then went to the dealership I personally preferred to buy from and asked if they could match it. Not wanting to lose a sale to the dealership down the road, they did, even going under invoice.
The first dealership did try to undervalue my trade a little but I quickly got them back up to the number I was happy with. Other than that, it was no questions asked. They did try to stick to the "this price protection is only good for vehicles in stock" but since they had exactly 1 4Runner in stock (and it was a TE) they couldn't tout that line too much.
Good luck, I'll be looking forward to seeing more 5th Gens on the road in Florida (so far, I've seen only 2).